Curable silicone compositions which are cured by a hydrosilylation reaction are used to seal, cover, or adhere optical semiconductor elements in optical semiconductor devices. A curable silicone composition comprising a diorganopolysiloxane having at least two silicon-bonded alkenyl groups per molecule, an organopolysiloxane with a resin structure having a vinyl group, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a platinum metal-type catalyst is proposed in Japanese Unexamined Patent Application Publication No. 2000-198930A as such a curable silicone composition.
However, such a curable silicone composition has a problem in that it cannot sufficiently inhibit the discoloration of silver electrodes or a silver-plated substrate in the optical semiconductor device due to a sulfur-containing gas such as hydrogen sulfide in the air.
A curable silicone composition which contains a tetrazole compound having at least one type of functional group selected from the group consisting of amino groups, amide groups, carbonyl groups, carboxyl groups, and thiol groups in order to impart a silicone cured product with flame retardance is proposed in Japanese Unexamined Patent Application Publication No. H11-29709A, and a hydrosilylation reaction is also disclosed as the curing mechanism thereof.
However, although it is described in Japanese Unexamined Patent Application Publication No. H11-29709 that such a curable silicone composition can be used in electrical or electronic parts, there was no suggestion of an application for sealing, covering, or adhering an optical semiconductor element.